So far, so calm: despite predictions that this year's Atlantic hurricane season would be unusually busy, the season has entered its second half and a hurricane is yet to form.

On 23 May, the National Oceanic and Atmospheric Administration (NOAA) said it was "forecasting an active or extremely active season this year", because it was expecting bad weather in west Africa that would move westwards; warmer-than-average water temperatures in the Atlantic Ocean and Caribbean Sea; and the absence of El Nino, the phenomenon that produces unusually warm water temperatures in the tropical Pacific Ocean and affects Atlantic weather patterns.

The federal agency said there was a 70% likelihood of 13 to 20 named storms producing seven to 11 hurricanes, of which three to six could be major. Even NOAA's revised outlook, issued on 8 August, anticipated three to five major hurricanes.

The hurricane season began on 1 June and ends on 30 November. So far this year there have been seven named storms, causing more than a dozen deaths in Mexico.

Dennis Feltgen, a spokesman for the National Hurricane Center, told the Guardian in an email that since records began in 1851, the first Atlantic hurricane of the year has formed after 7 September only 13 times. The all-time record latest is 8 October, which happened in 1905. An average year would have seen the development of three hurricanes by early September. Last month was the first time since 2002 that August passed without a hurricane.

If the first hurricane of 2013 gathers after 8am ET on Wednesday, it will be the latest debutant to form since the satellite tracking era began in the mid-1960s.

However, Feltgen warned that the quiet opening half of the season was no guarantee of a hurricane-free second period and that there is still ample time for forecasts to be proved right. "We are at mid-point of the six-month hurricane season," he said. "It is a mistake to believe that the second half of the season would resemble the first half. With half of the season to go through yet, no one should let their guard down."

He said that contributing factors to the absence of hurricanes so far are dry, stable and sinking air over the central and eastern tropical Atlantic Ocean, dust originating from the Sahara and wind shear (changes in wind speed and direction). These cause storms to dissipate.

Hurricane Sandy, which last year killed more than 180 people and caused immense damage in the US, Canada and Caribbean, did not develop into a hurricane until 23 October. It made landfall as a storm along the New Jersey coast six days later.

13 September will mark the five-year anniversary of Hurricane Ike arriving at the Texas coast. It was blamed for about 200 deaths in the US and Haiti and caused widespread property destruction, becoming the third-costliest hurricane in US history, after Sandy and Katrina, which hit the Gulf coast in 2005.

The latest forecast from the National Hurricane Center indicates that a system currently moving west over Africa has an 80% chance of developing into an Atlantic tropical cyclone over the next five days.